1. Field of the Invention
The present invention relates to a communication robot capable of communicating with people, and more particularly to a communication robot that can naturally express motions of its movable parts or make a speech.
2. Description of the Related Art
A robot has been conventionally known which determines its behavior based on an external situation and its internal status in order to enhance the amusement property for a pet robot (e.g. refer to Unexamined Japanese Patent Application Publication No. 2004-283958, paragraphs 0136-0148, FIG. 18). A robot disclosed in Unexamined Japanese Patent Application Publication No. 2004-283958 has a plurality of behavior describing modules (schemes) in which actions having objectives, such as “exploring”, “eating”, and “playing” are described. Each scheme calculates, by using a predetermined function, an activation level AL of an action, which is the degree of execution priority of the scheme, in response to a change in the internal status of the robot or an external stimulus. Generally, the robot selects a scheme that has the highest AL, and expresses an action that corresponds to the scheme.
For example, the robot selects a scheme in which an action “kick a ball” is described when a user says to the robot “kick the ball” as a predetermined external stimulus. The selected scheme calculates the AL of the action so as to grasp how willing the robot is to perform the action, and determines whether or not the robot obeys the user's instruction based on the value of the AL. When the value of the AL is positive the robot obeys the user's instruction. In contrast, when the value of the AL is negative, the robot expresses a negative desire that it does not want to perform the action by emitting a predetermined sound “No, I don't want to” which notifies the user of the rejection of the action. As described above, the robot does not obey the user's instruction depending on the value of the AL of the action, which enhances the entertainment property of the robot.
However, since the robot disclosed in Unexamined Japanese Patent Application Publication No. 2004-283958 selects, among a plurality of predetermined schemes, a scheme to be executed, actions expressed by the robot are monotonous. Furthermore, the robot stays still in a resting state when the robot does not perform any action specified by the schemes, which makes the robot appear to behave unnaturally.
Some robots (communication robot) are required to perform actions to execute various tasks efficiently, such as a transportation task or a guide task while communicating with people. In this case, if actions expressed by the robot are monotonous, a user may not have a sense of affinity but a sense of discomfort to the robot, which may become an obstacle for the communication. Therefore, the communication robot is desired to be able to express a variety of actions in addition to the actions for efficiently executing the tasks.